1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method which determines a scaling factor from image data of original images scanned by an image input apparatus on a pixel basis or image data sent by a communication part, and detects a specific image in the image data. It also relates to an image forming apparatus which nullifies image data containing a specific image by using such an image processing apparatus and an image processing method.
2. Description of the Related Art
In recent years, a system as described below has been proposed for application to image forming apparatuses such as full color copiers. This system in advance embeds a specific pattern such as two-dimensional codes in publications, important papers, valuable papers, or the like and recognizes the pattern to prevent illicit use such as unauthorized duplication of publications.
In principle, a copier duplicates an original put in a predetermined place to exactly the same size as its original size or according to a specified scaling factor. Accordingly, an apparatus for recognizing a specific pattern in the copier can easily determine whether input image data is scaled, and its scaling factor if scaled, and can execute identification operations based on the scaling factor information.
On the other hand, unlike a copier, a printer is connected to an external apparatus such as a personal computer and image data to be outputted is sent from the external apparatus. A conceivable case is to read an original having a specific pattern embedded in advance into a memory within a personal computer by a reader such as a scanner and send the original to a printer as image data after scaling it by several percent. In such a case, an apparatus for recognizing a specific pattern within the printer judges that the specific pattern in the scaled image data is different from an intended specific pattern in size because the scaling factor is unknown. As a result, the specific pattern in the scaled image data may not be recognized as a specific pattern to be detected.
Techniques for preventing a specific pattern from being unrecognizable are disclosed in, e.g., Japanese Published Unexamined Patent Applications No. Hei 9-81729 and Hei 10-126614. The techniques allow an image recognition apparatus for recognizing a given specific pattern to calculate a scaling factor. The technique described in Japanese Published Unexamined Patent Application No. Hei 9-81729 uses a plurality of reference images, such as an image having an average or typical characteristic of a specific pattern to be recognized, an image having a maximum characteristic, and an image having a minimum characteristic. Matching is performed between the plurality of reference images and an object to be recognized, and a peak matching position and a matching level are obtained. Interpolation processing is performed using the results to calculate a scaling factor.
However, with this technique, other than circular images cannot be used as object images to be recognized. That is, in the case of non-circular object images or object images composed of a plurality of partial images which are not circular as a whole, images rotated intentionally or by skew may have been inputted. To provide for such a case, matching processing must be performed for rotated images. However, the matching processing for rotated images would require large-scale circuits if embodied by hardware, and huge amounts of computation processing if embodied by software. To correctly calculate a scaling factor from circular images only, large circular images have to have been formed in an image, posing a problem that image design is impaired.
The technique described in Japanese Published Unexamined Patent Application No. Hei 10-126614 detects a given mark from input image data and estimates the scaling factor of the input image data from the size of the mark. This literature detects a mark as large as 16 mm in diameter and estimates a scaling factor from the size of the mark. However, use of such a large mark would impair image design as described above. If a mark as small as about 1 mm is used and an input image is subjected to image resolution conversion (from 600 dpi to 100 dpi) according to the literature, the diameter of a mark of scaling factor 100% will change from 24 dots (600 dpi) to 4 dots (100 dpi). Such a small diameter is useless to correctly estimate a scaling factor. For example, scaling factors from 90 to 110% produce the same diameter of 4 dots, so that a scaling factor cannot be determined. If an original image contained a dummy mark that is the same as a mark in shape but is different from it in size, it would become more difficult to determine a scaling factor.
The present invention has been made in consideration of the above-described situation and its object is to provide an image processing apparatus and an image processing method which are capable of correctly determining the scaling factor of an input image containing a specific image composed of a predetermined number of partial images, an image processing apparatus and an image processing method which are capable of identifying the specific image based on the scaling factor, and an image forming apparatus which nullifies the image containing the specific image.
The present invention extracts, from an input image containing a specific image composed of a predetermined number of partial images that may have been scaled, the characteristic of the partial images, and determines the scaling factor of the input image from information of an area in which a predetermined number of images exist, the images being extracted as partial images based on the characteristic of the partial images. Since a scaling factor is thus determined from an area where a plurality of partial images making up a specific image exist, the partial images can be extracted from the input image regardless of a scaling factor and a scaling factor can be correctly determined from information of an area where the extracted partial images exist. A large specific image can be formed by, e.g., small partial images so that a scaling factor can be correctly determined without impairing image design. The partial images can have an identical shape and an identical size.
Furthermore, with consideration of the thus determined scaling factor of the input image, by comparing the distribution of the partial images with the specific image, it is judged whether the specific image is contained in the input image or not. By this process, after correctly determining the scaling factor of the scaled input image, it can be determined whether the specific image exists in the input image or not.
By providing such an image processing apparatus or an image processing method in an image forming apparatus as a recognition part, a specific image, if it exists in inputted image data, can be nullified. In this case, even if the inputted image data is for a scaled image, a scaling factor can be correctly determined as described above and the existence of a specific image can be judged, so that image data containing the specific image can be correctly nullified.